A Distributed Oscillator Based All-Digital PLL With a 32-Phase Embedded Phase-to-Digital Converter

This paper presents a wide-bandwidth, low-noise 4 GHz All-Digital PLL. It uses a rotary traveling wave oscillator (RTWO) as the oscillator core. By using multiphase signals available from the RTWO, the analog phase information is directly converted into the digital domain. Unlike the conventional time-to-digital converter (TDC) approach, it eliminates power hungry inverter delay chains as well as real time period normalization. The proposed approach significantly simplifies the ADPLL architecture while maintaining excellent phase noise. The PLL is implemented in a 65 nm CMOS process. The 32-phase embedded phase-to-digital converter (PDC) achieves 2π/64 phase resolution. The measured in-band phase noise is -108 dBc/Hz at 4 GHz with a 78 MHz reference and a 1 MHz loop bandwidth.